Field of the Invention
The present invention relates to a touch screen, a touch panel, a display device and an electronic device.
Description of the Background Art
A touch panel is a device which detects a touch of a finger or the like and specifies a position coordinate of a touched position. The touch panel is gaining attention as one of good user interface means. Currently, touch panels of various types such as a resistive type and a capacitive type are made into products. Generally, a touch panel includes a touch screen in which a touch sensor is built, and a detection device which specifies a touched position coordinate based on a signal from the touch screen.
One of the capacitive touch panels includes a projected capacitive touch panel (see, for example, Japanese Patent Application Laid-Open No. 2012-103761). Such a projected capacitive touch panel can detect a touch even when a front surface side of the touch screen in which a touch sensor is built is covered by a protection plate such as a glass plate having the thickness of about several mm. The touch panel of this type allows the protection plate to be arranged in the front surface and, consequently, has good toughness. Further, this touch panel can detect a touch with a glove put on. Furthermore, the touch panel does not include a movable portion and therefore have a long operating life.
The projected capacitive touch panel includes, for example, a first series of conductor elements which are formed on a thin dielectric film, and a second series of conductor elements which are formed on the first series of conductor elements across an insulating film as detection wirings which detect an electrostatic capacitance. Each conductor element does not electrically contact with each other, and a plurality of intersections are formed between the conductor elements. A detection circuit detects an electrostatic capacitance formed between a pointer such as a finger, and the first series of conductor elements and the second series of conductor elements which are the detection wirings to specify a position coordinate of a position touched by the pointer. This detection type is generally called a self-capacitance detection type (see, for example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 9-511086 (1997)).
Further, for example, there is a detection method of specifying a touched position coordinate by, for example, detecting a change in an electric field between a plurality of row wirings which composes a first electrode and is provided to extend in a row direction and a plurality of column wirings which composes a second electrode and is provided to extend in a column direction, i.e., by detecting a change in a mutual capacitance. This detection method is generally called a mutual capacitance detection type (see, for example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-526831).
In either case of the self-capacitance type and the mutual capacitance type, there is generally used a method, in which when a pointer such as a finger touches a planar region (detection cell) partitioned in a grid pattern by row wirings and column wirings, a touched position coordinate is specified based on a balance between a detection value of a sensor block and a detection value of a detection cell near the sensor block.
Further, recently, a mesh is formed by using low-resistance metal for detection wirings (see, for example, Japanese Patent Application Laid-Open No. 2010-061502) to realize a larger and high-performance touch screen by taking advantage of lower-resistance characteristics than transparent electrodes such as ITO.
According to a configuration where a mesh of row wirings formed as micro wirings and a mesh of column wirings formed as micro wirings three-dimensionally intersect across an insulating film as disclosed in, for example, Japanese Patent Application Laid-Open No. 2010-061502, local cross capacitances at three-dimensional intersection portions of row wirings and column wirings are low. Hence, there is a problem that a conductor such as finger approaches the touch panel, a potential difference is likely to be produced when electrostatic discharge occurs and dielectric breakdown is likely to occur.